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MD. Saidur Rahman KohinooR
CHAPTER 1
Introduction Review Questions 1. Identify the five components of a data communications system? Ans: The five components of a data communication system are the sender, receiver, transmission medium, message, and protocol. 2. What are the advantages of distributed processing? Ans: The advantages of distributed processing are security, access to distributed databases, collaborative processing, and faster problem solving. 3. What are the three criteria necessary for an effective and efficient network? Ans: The three criteria are performance, reliability, and security. 4. What are the advantages of a multipoint connection over a point-to-point connection? Ans: Advantages of a multipoint over a point-to-point configuration (type of connection) include ease of installation and low cost. 5. What are the two types of line configuration? Ans: Line configurations (or types of connections) are point-to-point and multipoint. 6. Categorize the four basic topologies in terms of line configuration. Ans: We can divide line configuration in two broad categories: a. Point-to-point: mesh, star, and ring. b. Multipoint: bus 7. What is the difference between half-duplex and full-duplex transmission modes? Ans: In half-duplex transmission, only one entity can send at a time; in a full-duplex transmission, both entities can send at the same time. 8. Name the four basic network topologies, and cite an advantage of each type. Ans: We give an advantage for each of four network topologies: a. Mesh: secure b. Bus: easy installation c. Star: robust d. Ring: easy fault isolation 9. For n devices in a network, what is the number of cable links required for a mesh, ring, bus, and star topology? Ans: The number of cables for each type of network is: a. Mesh: n (n – 1) / 2 b. Star: n c. Ring: n – 1
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MD. Saidur Rahman KohinooR
d. Bus: one backbone and n drop lines 10. What are some of the factors that determine whether a communication system is a LAN or WAN? Ans: The general factors are size, distances (covered by the network), structure, and Ownership 11. What is an internet? What is the Internet? Ans: An internet is an interconnection of networks. The Internet is the name of a specific worldwide network 12. Why are protocols needed? Ans: A protocol defines what is communicated, in what way and when. This provides accurate and timely transfer of information between different devices on a network. 13. Why are standards needed? Ans: Standards are needed to create and maintain an open and competitive market for manufacturers, to coordinate protocol rules, and thus guarantee compatibility of data communication technologies.
Exercises 14. What is the maximum number of characters or symbols that can be represented by Unicode? Ans: Unicode uses 32 bits to represent a symbol or a character. We can define 232 different symbols or characters. 15. A color image uses 16 bits to represent a pixel. What is the maximum number of different colors that can be represented? Ans: With 16 bits, we can represent up to 216 different colors. 16. Assume six devices are arranged in a mesh topology. How many cables are needed? How many ports are needed for each device? Ans: a. Cable links: n (n – 1) / 2 = (6 × 5) / 2 = 15 b. Number of ports: (n – 1) = 5 ports needed per device 17. For each of the following four networks, discuss the consequences if a connection fails. a. Five devices arranged in a mesh topology b. Five devices arranged in a star topology (not counting the hub) c. Five devices arranged in a bus topology d. Five devices arranged in a ring topology Ans: a. Mesh topology: If one connection fails, the other connections will still be working. b. Star topology: The other devices will still be able to send data through the hub; there will be no access to the device which has the failed connection to the hub. c. Bus Topology: All transmission stops if the failure is in the bus. If the drop-line fails, only the corresponding device cannot operate. d. Ring Topology: The failed connection may disable the whole network unless it is a dual ring or there is a by-pass mechanism. www.facebook.com/kohinoor11
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MD. Saidur Rahman KohinooR
18. You have two computers connected by an Ethernet hub at home. Is this a LAN, a MAN, or a WAN? Explain your reason. Ans: This is a LAN. The Ethernet hub creates a LAN because of we know that a local area network (LAN) is a computer network that is designed for a limited geographic area such as a building or a campus or an isolated network to connect computers. 19. In the ring topology in Figure 1.8, what happens if one of the stations is unplugged?
Ans: Theoretically, in a ring topology, unplugging one station, interrupts the ring. However, most ring networks use a mechanism that bypasses the station; the ring can continue its operation. 20. In the bus topology in Figure 1.7, what happens if one of the stations is unplugged?
Ans: In a bus topology, no station is in the path of the signal. Unplugging a station has no effect on the operation of the rest of the network. 21. Draw a hybrid topology with a star backbone and three ring networks.
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MD. Saidur Rahman KohinooR
Ans:
22. Draw a hybrid topology with a ring backbone and two bus networks. Ans:
23. Performance is inversely related to delay. When you use the Internet, which of the following applications are more sensitive to delay? a. Sending an e-mail b. Copying a file c. Surfing the Internet Ans: a. E-mail is not an interactive application. Even if it is delivered immediately, it may stay in the mail-box of the receiver for a while. It is not sensitive to delay. b. We normally do not expect a file to be copied immediately. It is not very sensitive to delay. c. Surfing the Internet is the an application very sensitive to delay. We except to get access to the site, we are searching.
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24. When a party makes a local telephone call to another party, is this a point-to-point or multipoint connection? Explain your answer. Ans: In this case, the communication is only between a caller and the caller. A dedicated line is established between them. The connection is point-to-point. 25. Compare the telephone network and the Internet. What are the similarities? What are the differences? Ans: The telephone network was originally designed for voice communication; the Internet was originally designed for data communication. The two networks are similar in the fact that both are made of interconnections of small networks. The telephone network, as we will see in future chapters, is mostly a circuit-switched network; the Internet is mostly a packet-switched network.
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